As an introduction to the problems solved by the present invention, consider conventional electrostatographic printing apparatus such as that used in printers, facsimile machines, and copiers, to name a few common applications. In such applications, operations can include unattended operation for long periods of time and large batch operations involving many printed pages between occasions when an operator can examine the print quality.
A lack of a consumable printing supply such as toner can result in the onset of unacceptable print quality with consequential waste of resources while unacceptable quality printing continues. Manual intervention is often required to renew the supply and, if possible, restart the batch operation. In the case of facsimile machines and network printers, further consequential costs accrue for an interruption of business in order to notify the appropriate users who are able to restart particular transmissions and automated operations.
Toner for an electrostatographic printing apparatus is conventionally packaged either in a replaceable cartridge having additional precision mechanical and electronic assemblies, or in bulk for use with a hopper receptacle in the apparatus. Replenishment of toner in most cases is an operation requiring some personal and equipment safety training and some familiarity with the internals of the apparatus. In the case of bulk toner, the operator must understand correct methods of handling the toner material itseft. If a lack of sufficient toner is first noticed during a batch operation, trained operators may not be immediately available to properly suspend wasteful printing or replenish the supply. If, on the other hand, a fresh toner cartridge is added prior to beginning a batch operation, unused toner in the removed cartridge is usually discarded.
Waste of organizational resources and of printing supplies adds to the actual per page cost of printing and has a detrimental impact on the timeliness and quality of business communications in general.
In view of the problems described above and related problems that consequently become apparent to those skilled in the applicable arts, the need remains in printing apparatus for improved systems for sensing consumption of a printing supply.